1. Field of the Invention
The present invention relates to a method of mounting an integrated circuit having a plurality of leads on a printed circuit board, and more particularly, to a method of mounting an integrated circuit of a tape carrier package (TCP) type on a printed circuit board (PCB).
2. Description of the Related Art
Recently, as the semiconductor technologies have developed, integrated circuits having complex functions have been introduced. As an example of such integration, the integration of a central processing unit (CPU) which performs very important functions of the microcomputer has progressed rapidly. In addition, to emit heat from the integrated circuit having complex functions, the shape of the package of the integrated circuit has been changed. For example, the CPU of a microcomputer has been developed from an 8086 8-bit processor to 80386, 80486 and 80586 thirty-two-bit processors through 80286 sixteen-bit processors. As the CPU having higher efficiencies have been developed, the number of the leads of the CPU rapidly increases. Moreover, as the density of the leads increases, new technologies for mounting the CPU on the printed circuit board have been developed.
Recent efforts in the art are exemplified by: U.S. Pat. No. 4,283,847 to May, entitled Circuit Board Assembly, U.S. Pat. No. 5,631,497 to Miyano et al., entitled Film Carrier Tape And Laminated Multi-Chip Semiconductor Device Incorporating The Same, U.S. Pat. No. 5,504,988 to Avery et al., entitled Apparatus For Mounting Surface Mount Devices To A Circuit Board, U.S. Pat. No. 5,479,694 to Baldwin, entitled Method For Mounting Integrated Circuits Onto Printed Circuit Boards And Testing, U.S. Pat. No. 5,372,972 to Hayashi et al., entitled Method Of And An Apparatus For Processing A Lead Frame, U.S. Pat. No. 5,369,879 to Goeschel et al., entitled Method Of Mounting A Semiconductor Device To A Heat Sink, U.S. Pat. No. 5,153,981 to Soto, entitled Universal Apparatus For Forming Lead Wires, U.S. Pat. No. 5,646,444 to Bartlett et al., entitled Apparatus And Method For Mounting A Component To An Electrical Circuit, and U.S. Pat. No. 5,673,479 to Hawthorne, entitled Method For Mounting A Microelectronic Circuit Peripherally-Leaded Package Including Integral Support Member With Spacer.
In recent days, as the high efficiency has been required even in a small computer such as a notebook computer, a Pentium (TM) processor which functions as the CPU is mounted and will continue to be mounted in compliance with the requests of users. In the case of notebook computer, however, as the miniaturization is needed, a small-sized integrated circuit is preferred. On the contrary, as the external size becomes smaller, the package form of the integrated circuit is important because of the radiation. A Pentium (TM) processor of the TCP type will be explained as an integrated circuit in an embodiment of a method for mounting the integrated circuit on the PCB of the present invention.
Conventionally, an integrated circuit of the TCP type is a very small compartment which includes 320 pins and has a spacing of 0.2 mm between the leads. Moreover, the integrated circuit of the TCP type is formed without a wire bonding which is used in the conventional semiconductor chip. As a result, as the size of the circuit is small, and the size of the printed circuit board can be smaller.
In an integrated circuit of the TCP type, at the center of a polyimide film, a semiconductor chip for performing a practical function of the integrated circuit is located. The semiconductor chip is attached to the polyimide film and it is slightly thicker than the polyimide film. Leads from the semiconductor chip are formed on the back side of the polyimide film with a pattern shape thereby maintaining the insulation between the leads and protecting them from external shock. Slots are formed at positions spaced apart from the edges of the polyimide film so as to face each edge of the semiconductor chip and a portion of the leads are exposed. An integrated circuit of the TCP type with this structure is supplied from the manufacturer with a plastic carrier for protection, and is mounted on the PCB. Once the PCB on which the operation is finished in the previous process is transported by a transporting guide rail to be provided, the PCB is fixed and a flux is evenly spread over the lead patterns on the PCB corresponding to the positions where the leads of the integrated circuit are to be soldered. By transporting the integrated circuit in which the cutting and forming are performed by a separate process to the PCB on which the flux is spread, the leads of the integrated circuit are aligned to correspond accurately to the lead patterns on the PCB. A hot bar at a high temperature presses the leads of the integrated circuit located on the lead patterns of the PCB so as to solder the leads of the integrated circuit on the lead patterns. Since solder has previously been coated on the lead patterns of the integrated circuit on the PCB during the previous process, it is possible to perform the soldering operation.
After loading the integrated circuit which is received by the plastic carrier in the tray into a cutting and forming unit for cutting and forming the leads into the integrated circuit, the integrated circuit leads are cut to a predetermined size by a cutting and forming tool suitable to lead patterns on the PCB. The cutting and forming tool is lowered on the integrated circuit and cuts the polyimide film which is located at the other side of the semiconductor chip centered around the slot. As a result, the array of the leads is properly performed after the cutting operation is finished.
According to earlier mounting method however, the leads can be misaligned when the hot bar presses the leads of the integrated circuit at a high temperature during the soldering step. As a result, shorts between adjacent leads can frequently occur and as the hot bar presses the leads directly, it is possible to damage a thin lead. Moreover, the life of the leads can be reduced though they are soldered and shorts between the leads can occur.
The PCB employing the earlier mounting method typically has a groove having a rectangular shape similar to the size of the semiconductor chip of the integrated circuit located at the position for mounting the integrated circuit. The groove is used to mount a heat sink which emits heat generated when the integrated circuit operates. Since the backside of the semiconductor chip of the integrated circuit protrudes slightly from the polyimide film, the backside of the semiconductor chip and the beat sink are connected by attaching conductive adhesive pads to the protruding part of the semiconductor chip and one end of the heat sink. The rectangular groove acts as a spacer for the connection. It takes a considerable amount of time however, to attach the heat sink and the operation is very difficult.